GTK4 Menubar not showing

Question

I'm trying to create a basic menubar. I've tried some sample code found on the internet and nothing seems to work. It all compiles but the menuBar simply doesn't appear when I run the program. The following two pieces of code only produce a blank window. What could be wrong?

Any help is greatly appreciated.

#include <gtk/gtk.h>
  
  static void
  quit_activated(GSimpleAction *action, GVariant *parameter, gpointer user_data) {
    GApplication *app = G_APPLICATION (user_data);

    g_application_quit (app);
 }

 static void
 app_activate (GApplication *app, gpointer user_data) {
   GtkWidget *win = gtk_application_window_new (GTK_APPLICATION (app));
   gtk_window_set_title (GTK_WINDOW (win), "menu1");
   gtk_window_set_default_size (GTK_WINDOW (win), 400, 300);

   GSimpleAction *act_quit = g_simple_action_new ("quit", NULL);
   g_action_map_add_action (G_ACTION_MAP (app), G_ACTION (act_quit));
   g_signal_connect (act_quit, "activate", G_CALLBACK (quit_activated), app);

   GMenu *menubar = g_menu_new ();
   GMenuItem *menu_item_menu = g_menu_item_new ("Menu", NULL);
   GMenu *menu = g_menu_new ();
   GMenuItem *menu_item_quit = g_menu_item_new ("Quit", "app.quit");
   g_menu_append_item (menu, menu_item_quit);
   g_object_unref (menu_item_quit);
   g_menu_item_set_submenu (menu_item_menu, G_MENU_MODEL (menu));
   g_menu_append_item (menubar, menu_item_menu);
   g_object_unref (menu_item_menu);

   gtk_application_set_menubar (GTK_APPLICATION (app), G_MENU_MODEL (menubar));
   gtk_application_window_set_show_menubar (GTK_APPLICATION_WINDOW (win), TRUE);
   gtk_window_present (GTK_WINDOW (win));
 /*  gtk_widget_show (win); is also OKay instead of gtk_window_present. */
 }

 #define APPLICATION_ID "com.github.ToshioCP.menu1"

 int
 main (int argc, char **argv) {
   GtkApplication *app;
   int stat;

   app = gtk_application_new (APPLICATION_ID, G_APPLICATION_FLAGS_NONE);
   g_signal_connect (app, "activate", G_CALLBACK (app_activate), NULL);

   stat =g_application_run (G_APPLICATION (app), argc, argv);
   g_object_unref (app);
   return stat;
}

#include <gtk/gtk.h>

static void action_clbk ( GSimpleAction *simple_action, G_GNUC_UNUSED GVariant *parameter, G_GNUC_UNUSED gpointer *data )
{
    g_print ( "The action %s was clicked.\n", g_action_get_name ( G_ACTION ( simple_action ) ) );
}

static void activate ( GApplication *app, G_GNUC_UNUSED gpointer *data )
{
    GtkWidget *win;
    GSimpleAction *act_connect;
    GSimpleAction *act_disconnect;

    /// ***
    GMenu *menu_bar;
    GMenu *network_menu;
    GMenu *server_menu;

    /// ***
    GMenuItem *menu_item_connect;
    GMenuItem *menu_item_disconnect;

    /// *** Menu Bar
    menu_bar = g_menu_new();

    /// *** Network_Menu
    network_menu = g_menu_new();
    g_menu_append_submenu ( menu_bar, "Network", G_MENU_MODEL ( network_menu ) );

    /// *** Server_Menu
    server_menu = g_menu_new();
    g_menu_append_submenu ( network_menu, "Server", G_MENU_MODEL ( server_menu ) );
    /// ***
    win = gtk_application_window_new ( GTK_APPLICATION ( app ) );
    gtk_window_set_title ( GTK_WINDOW ( win ), "IRC Client" );
    gtk_window_set_default_size ( GTK_WINDOW ( win ), 400, 400 );

    /// *** Create Connect and Disconnect Actions
    act_connect    = g_simple_action_new ( "connect", NULL );
    act_disconnect = g_simple_action_new ( "disconnect", NULL );

    /// *** Add them to the ActionMap
    g_action_map_add_action ( G_ACTION_MAP ( app ), G_ACTION ( act_connect ) );
    g_action_map_add_action ( G_ACTION_MAP ( app ), G_ACTION ( act_disconnect ) );

    /// *** Connect them to the activate Signal
    g_signal_connect ( act_connect,    "activate", G_CALLBACK ( action_clbk ), NULL );
    g_signal_connect ( act_disconnect, "activate", G_CALLBACK ( action_clbk ), NULL );

    /// *** Create the Connect Item
    menu_item_connect = g_menu_item_new ( "Connect", "app.connect" );
    g_menu_append_item ( server_menu, menu_item_connect );

    /// *** Create the Disconnect Item
    menu_item_disconnect = g_menu_item_new ( "Disconnect", "app.disconnect" );
    g_menu_append_item ( server_menu, menu_item_disconnect );

    /// ***
    gtk_application_set_menubar             ( GTK_APPLICATION ( app ), G_MENU_MODEL ( menu_bar ) );
    gtk_application_window_set_show_menubar ( GTK_APPLICATION_WINDOW ( win ), TRUE );

    /// ***
    gtk_window_present ( GTK_WINDOW ( win ) );

    /// *** Clean
    g_object_unref ( act_connect );
    g_object_unref ( act_disconnect );
    g_object_unref ( menu_item_connect );
    g_object_unref ( menu_item_disconnect );
    g_object_unref ( server_menu );
    g_object_unref ( network_menu );
    g_object_unref ( menu_bar );
}

int main ( int argc, char **argv )
{
    GtkApplication *app;
    int stat;

    /// ***
    app = gtk_application_new ( "com.ircclient", G_APPLICATION_FLAGS_NONE );
    g_signal_connect ( app, "activate", G_CALLBACK ( activate ), NULL );

    /// ***
    stat = g_application_run ( G_APPLICATION ( app ), argc, argv );
    g_object_unref ( app );

    /// ***
    return stat;
}